1. Field of the Invention
The present invention relates to novel glass composition comprising oxygen and nitrogen, hereinafter oxygen/nitrogen glass compositions, and more especially, to novel oxygen/nitrogen magnesium aluminosilicate compositions.
This invention also relates to precursors of such novel glass compositions and to the use of the novel glasses for the production of vitroceramic compositions and composite materials incorporating these vitroceramics.
2. Description of the Prior Art
It is known to this art that the presence of nitrogen in a vitreous matrix considerably modifies the physical and chemical properties of the glasses. Thus, in the case of oxygen/nitrogen glasses, there is an increase in the leaching resistance, an improvement in the mechanical characteristics, such as hardness and elastic moduli (Young's modulus, shear modulus, etc.), a reduction in their thermal expansion coefficient, a viscosity increase and a high Hruby factor value.
The increase in these latter two characteristics (viscosity, Hruby factor) results in a reduction in the recrystallization rate of the oxygen/nitrogen glasses. Therefore, this phenomenon is easier to control and the evolution of the crystallization, i.e., the characteristics of the vitroceramics, is slower during subsequent heat treatments.
With respect to such vitroceramic compositions, it is of interest to provide compositions of this type having very low expansion coefficients. Moreover, in the case of a composite material comprising a vitroceramic matrix and fibrous reinforcing material, the presence of nitrogen within the matrix is, as a result of its being a reducing agent, a desirable factor in regard to the protection of non-oxidized ceramic fibers.
It has already been proposed to prepare oxygen/nitrogen magnesium aluminosilicate glasses. However, the known processes generally permit the preparation of only very specific compositions. And even those processes permitting the preparation of possibly broader compositional ranges do not enable the production of vitroceramics therefrom that have an acceptable coefficient of expansion.